39 lines
1.3 KiB
PHP
39 lines
1.3 KiB
PHP
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.macro INIT_NES
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sei ; Disable all IRQ interrupts
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cld ; Clear decimal mode (not supported by the NES)
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ldx #$FF
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txs ; Initialize the stack pointer at address $FF
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inx ; Increment X, causing a rolloff from $FF to $00
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stx PPU_CTRL ; disable NMI
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stx PPU_MASK ; disable rendering
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stx $4010 ; disable DMC IRQs
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lda #$40
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sta $4017 ; disable APU frame IRQ
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Wait1stVBlank:
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bit PPU_STATUS
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bpl Wait1stVBlank
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txa ; A = 0
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ClearRAM:
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sta $0000,x ; Zero RAM addresses from $0000 to $00FF
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sta $0100,x ; Zero RAM addresses from $0100 to $01FF
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sta $0200,x ; Zero RAM addresses from $0200 to $02FF
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sta $0300,x ; Zero RAM addresses from $0300 to $03FF
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sta $0400,x ; Zero RAM addresses from $0400 to $04FF
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sta $0500,x ; Zero RAM addresses from $0500 to $05FF
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sta $0600,x ; Zero RAM addresses from $0600 to $06FF
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sta $0700,x ; Zero RAM addresses from $0700 to $07FF
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inx
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bne ClearRAM
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Wait2ndVBlank:
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bit PPU_STATUS
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bpl Wait2ndVBlank ; bit-7 is 1
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.endmacro
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